The forward power discriminator functions the same as the reflected power discriminator except
the current and voltage sample are 180 out of phase. This results in a dc output voltage being at
maximum when the rf line is terminated in 50-ohms. Any other value of terminating impedance
will cause the dc output voltage to vary proportional to forward power, thereby causing the
monitored voltage to change.
b. Input Coupling and Resonator/Central Resonator/Output Resonator and Coupling. The input
coupling employs a fixed series inductor (L7) tapped into the input resonator (L8 and C12). This
form of coupling provides good coupling characteristics along with minimum resonator frequency
shift. The resonator circuit is composed of inductor L8 and variable capacitor C12. The variable
capacitor is mechanically linked to the top tuning knob on the front panel. The tuning knob is
used for selecting operating frequency and for coarse and rf tuning adjustments. The resonator
also supplies a voltage sample to the 90 phasing discriminator.